Fix #79099: OOB read in php_strip_tags_ex

Author: smalyshev

ext/standard/string.c

@@ -4866,7 +4866,7 @@ PHPAPI size_t php_strip_tags_ex(char *rbuf, size_t len, uint8_t *stateptr, const
 				if (state == 4) {
 					/* Inside <!-- comment --> */
 					break;
-				} else if (state == 2 && *(p-1) != '\\') {
+				} else if (state == 2 && p >= buf + 1 && *(p-1) != '\\') {
 					if (lc == c) {
 						lc = '\0';
 					} else if (lc != '\\') {
@@ -4893,7 +4893,7 @@ PHPAPI size_t php_strip_tags_ex(char *rbuf, size_t len, uint8_t *stateptr, const
 
 			case '!':
 				/* JavaScript & Other HTML scripting languages */
-				if (state == 1 && *(p-1) == '<') {
+				if (state == 1 && p >= buf + 1 && *(p-1) == '<') {
 					state = 3;
 					lc = c;
 				} else {
@@ -4920,7 +4920,7 @@ PHPAPI size_t php_strip_tags_ex(char *rbuf, size_t len, uint8_t *stateptr, const
 
 			case '?':
 
-				if (state == 1 && *(p-1) == '<') {
+				if (state == 1 && p >= buf + 1 && *(p-1) == '<') {
 					br=0;
 					state=2;
 					break;

ext/standard/tests/file/bug79099.phpt

@@ -0,0 +1,32 @@
+--TEST--
+Bug #79099 (OOB read in php_strip_tags_ex)
+--FILE--
+<?php
+$stream = fopen('php://memory', 'w+');
+fputs($stream, "<?\n\"\n");
+rewind($stream);
+var_dump(fgetss($stream));
+var_dump(fgetss($stream));
+fclose($stream);
+
+$stream = fopen('php://memory', 'w+');
+fputs($stream, "<\0\n!\n");
+rewind($stream);
+var_dump(fgetss($stream));
+var_dump(fgetss($stream));
+fclose($stream);
+
+$stream = fopen('php://memory', 'w+');
+fputs($stream, "<\0\n?\n");
+rewind($stream);
+var_dump(fgetss($stream));
+var_dump(fgetss($stream));
+fclose($stream);
+?>
+--EXPECT--
+string(0) ""
+string(0) ""
+string(0) ""
+string(0) ""
+string(0) ""
+string(0) ""